1. Field of the Invention
The present invention relates to a dental alginate impression material to be used for taking an impression in the oral cavity in the dentistry, which is set upon mixing two types of pastes, i.e., a main paste and a setting paste. In particular, the present invention relates to a dental alginate impression material that is superior in preservability, is free from change of viscosity of the main paste with time and from liquid separation of the setting paste, and does not cause a delay in setting time during the preservation.
2. Description of the Conventional Art
In the dentistry, as an impression material for taking an impression in the oral cavity during the preparation of a prosthesis, is widely used a dental alginate impression material. The dental alginate impression material includes one which is usually provided in the form of a powder containing an alginate, a gelling reaction material, a gelling adjustment material, and a filler as major components and is set by mixing with water during the use; and one which is provided in the form of two types of pastes, i.e., a main paste and a setting paste, and is set by mixing these pastes during the use. And, in recent years, for the reasons that the mixing is easy and that it is possible to achieve automatic mixing, and so on, a pasty alginate impression material comprising a main paste and a setting paste is frequently used.
In this pasty alginate impression material, usually, the main paste is constructed of a paste prepared by dissolving an alginate in water and adding a filler as a component for imparting shaping properties and hardness to the solution; and the setting paste is constructed of a paste comprising a mixture of calcium sulfate, as setting materials for the alginate, and a liquid substance such as liquid paraffin. These pasty alginate impression materials are easy for mixing, and can be continuously mixed and extruded by using an exclusive instrument. Accordingly, they are very convenient for dentists or hygienists and are frequently used.
However, the currently used pasty alginate impression material are poor in preservability. Further, the main paste thereof is remarkable in change of the viscosity with time, and the setting paste thereof is liable to cause separation between calcium sulfate and the liquid component. As a result, when the main paste is mixed with the setting paste, the mixture is liable to become poor, whereby inconvenience arises such that an accurate impression cannot be obtained. In addition, in the case where the viscosity changes, the fluidity of the mixed material also changes. As a result, there are inconveniences such that a minute impression cannot be taken or that dropping of the paste occurs in the depth of the throat. Moreover, the setting paste is remarkable in deterioration with time, and the setting time is delayed. As a result, it is not set within a usual holding time in the mouth, leading to causing an incomplete impression.
The present invention is aimed at developing a pasty dental alginate impression material comprising a main paste and a setting paste, which is superior in preservability, is free from change of viscosity of the main paste with time and from liquid separation and deterioration of the setting paste, and has no possibility to cause a delay in setting time during the preservation.
In order to achieve the above-described aim, we, the present inventors made extensive and intensive investigations. As a result, it has been found that, when one or two or more polysaccharides selected from the group consisting of carrageenan, pullulane, curdlan, xanthane gum, gellan gum, pectin, konjak glucomannan, xyloglucan, guar gum, gum arabic, and locust bean gum are added to the conventional main paste containing an alginate, water and a filler as major components, the change of viscosity with time is suppressed, while when polybutene is added to a setting paste containing calcium sulfate and a liquid component as major components, the liquid separation and deterioration are suppressed, leading to the accomplishment of the present invention.
Specifically, the present invention is concerned with a dental alginate impression material comprising two types of pastes of a main paste containing an alginate, water and a filler as major components and a setting paste containing calcium sulfate and a liquid component as major components, the both pastes being to be mixed and set, wherein the main paste further contains 0.01 to 15% by weight of one or two or more polysaccharides selected from the group consisting of carrageenan, pullulane, curdlan, xanthane gum, gellan gum, pectin, konjak glucomannan, xyloglucan, guar gum, gum arabic, and locust bean gum, and the setting paste further contains from 0.5 to 50% by weight of polybutene.
Of the alginate, water and filler used as the major components of the main paste according to the present invention, is used, as the alginate, at least one water-soluble salt such as sodium, potassium, ammonium and triethanolamine salts of alginic acid. The alginate is usually contained in an amount of from about 1 to 10% by weight in the main paste. As the water, any of ion exchanged water and distilled water may be used. Also, water subjected to sterilization treatment with sodium hypochlorite, etc. may be used. As the filler, is used at least one powder such as diatomaceous earth, silicicanhydride, talc, calcium carbonate, and perlite.
Of the calcium sulfate and liquid component used as the major components of the setting paste, is used a dihydrate or hemihydrate of clacium sulfate, as the calcium sulfate. As the liquid component, are used liquid paraffin, aliphatic alcohols, and fatty acids.
In the case where the composition is composed only of these components used for the usual pasty dental alginate impression material, the viscosity of the main paste changes with time as described above. Accordingly, in the present invention, one or two or more polysaccharides selected from the group consisting of carrageenan, pullulane, curdlan, xanthane gum, gellan gum, pectin, konjak glucomannan, xyloglucan, guar gum, gum arabic, and locust bean gum are added as a component for preventing the change of viscosity of the main paste with time. These polysaccharides are stable in the alginate aqueous solution and are hardly decomposed. Therefore, reduction of the viscosity of the paste hardly occurs.
Of these polysaccharides, carrageenan is one of seaweed polysaccharides and is an acidic polymer comprising galactose containing a sulfate group and an anhydro group. Pullulane, curdlan, xanthane gum, and gellan gum are obtained by separating and purifying polysaccharides produced by microorganisms such as yeast. Of these, is the most useful xanthane gum, which is a viscous polysaccharide produced by bacteria separated from a cabbage leaf surface. Pectin, konjakglucomannan, xyloglucan, guar gum, gum arabic, and locust bean gum are polysaccharides extracted from barks, seeds, leaf stems, subterranean stems, fruits, and the like of plants. Such one or two or more polysaccharides selected from the group consisting of carrageenan, pullulane, curdlan, xanthane gum, gellan gum, pectin, konjak glucomannan, xyloglucan, guar gum, gum arabic, and locust bean gum may be contained in an amount of 0.01 to 15% by weight in the main paste containing an alginate, water and a filler as major components. When the content of the polysaccharide(s) is less than 0.01% by weight, the effect for suppressing the change of viscosity of the main paste with time is insufficient. On the other hand, when it exceeds 15% by weight, the viscosity is too high so that the mixing becomes difficult, resulting in hindrance of the impression taking operation. Preferably, the content of the polysaccharide(s) is 0.1 to 3% by weight.
With respect to the setting paste, the currently used setting paste as described above, which contains calcium sulfate and a liquid component such as liquid paraffin, aliphatic alcohols, and fatty acids as major components, causes the separation of calcium sulfate, so that it is difficult to keep the setting paste as a homogenous paste. Thus, in the present invention, it is designed to prevent the separation of calcium sulfate from the liquid component by adding polybutene thereto.
This polybutene is a liquid polymer composed mainly of isobutylene and having a little amount of 1-butene copolymerized therewith. Usually, those having a number average molecular weight of 300 to 4,000 are used. When this polybutene is added to the setting paste, not only the viscosity of the liquid component increases, but also calcium sulfate is uniformly dispersed and stabilized in the liquid component, whereby the separation of calcium sulfate from the liquid component hardly occurs. Further, since calcium sulfate is uniformly dispersed in the setting paste, it is possible to prevent the calcium sulfate from change of properties during the preservation and the setting time from a delay. The polybutene may be contained in an amount of 0.5 to 50% by weight in the setting paste. When the content of the polybutene is less than 0.5% by weight, the calcium sulfate is separated from the liquid component. On the other hand, when it exceeds 50% by weight, not only the setting time becomes longer, but also the strength of the set material is lowered.
In addition, so far as the characteristics of the dental alginate impression material according to the present invention are not lost, the main paste may further contain various inorganic or organic coloring agents, antiseptics, various disinfectants, flavors or perfumes, and the like; and the setting paste may further contain retarders, pH regulators such as magnesium oxide or hydroxide, surfactants for improving the mixing properties with the main paste, fluorides for improving the model surface, and the like.